Abstract:

When the mechanical properties of oilwell cement are evaluated, one can analyze the cement-sheath integrity and choose the best cement depending on the pressure and temperature conditions. The analytical method is used because of its simplification and easy to use. The present model is linked to the development of a plastic zone around a tunnel realized by Panet (1976). Cement is considered as an elastic material whereas the geological formation behaves like an elasto-plastic material. After the elastic limit, a plastic zone of the formation is formed around the cement-sheath with a radius Rp. This radius is needed to evaluate because the plastic zone favors gas migration. In the SRC, the stress vs. displacement curvesof the formation and cement sheath at a given moment are plotted. The intersection of two curves defines the stable state of interface cement sheath-formation. If this stable point is in the plastic zone of the formation, a plastic zone is formed and gas migration occurs. The model allows evaluating the pertinent mechanical properties of cement at a given period to avoid damage cement sheath and the formation.